In an electronic imaging apparatus, such as a digital projector, light from each of three or more spectral bands, conventionally Red, Green, and Blue (RGB), is modulated and the modulated light output is combined on a front- or rear-projection screen or other display surface in order to provide a color image. Earlier electronic imaging apparatus employed broadband lamps and other polychromatic illumination sources to provide the colored light in each color channel. More recent systems utilize narrow-band solid-state light sources, notably Light Emitting Diodes (LEDs) and lasers as illumination sources. Using solid-state light sources of these types, it became possible to reduce some of the size and cost of color mixing components, as well as to improve color gamut, to increase optical efficiency, and to enhance the overall performance of the imaging device.
Digital projection apparatus form images by directing the color illumination onto a spatial light modulator (SLM), including devices such as a Liquid Crystal on Silicon (LCoS) device or a micromirror array, such as the Digital Light Processor (DLP) from Texas Instruments, Inc., Dallas, Tex. Other types of SLM include scanned linear modulators such as the grating light valve (GLV) from Silicon Light Machines, Inc., Sunnyvale, Calif. The color image that is formed is a composite of individually modulated red, green, and blue images; each color image is separately modulated, either at an SLM that is dedicated to a particular red, green, or blue color channel as part of a three-channel system, or at a single SLM that is time-shared between the three color channels, in what is known as a color-sequential imaging sequence or field sequential imaging.
Among factors in the cost/performance tradeoff for digital projector design are brightness, image quality and color gamut, and component count. Predictably, image quality and brightness can be optimized using a more costly design with separate color channels, each having its own illumination source and SLM. The color-sequential projector, with only a single SLM and without the need for color combination components, can be made more affordable, but only offers a fraction of the brightness possible with the three-channel system.
In addition to alternative projector designs, a number of different projector configurations are known in the art, including applications that employ multiple digital projectors. One application of interest is a so-called stitched-image projection system in which each projector forms a separate image and the separately formed images are then combined or stitched together to form a larger image. This imaging technique enables a large scale, high-resolution image to be formed and has advantages for increased brightness and increased resolution over single-projector systems.
Stitched image projection systems can still be costly, however, since several separate projectors are needed with separate light sources for each projector. It can be seen that there would be benefits to a stitched image projection system that offered improved performance at reduced cost and with more efficient use of illumination components.